by Jeremy Wilson, Utilidata Inc.
Conservation voltage reduction (CVR)-the operation of the electric distribution system in a way that delivers voltages to consumers at or near the lower bounds of statutory delivery standards-has been practiced in North America since the 1970s.
CVR benefits for utilities include peak demand reduction, energy savings and a decrease in technical and nontechnical line losses.
With the advent of the smart grid in the U.S. and its push by the American Recovery and Reinvestment Act of 2009, CVR has become known as an operational state of a technology and referred to as volt/VAR optimization (VVO) or integrated volt/VAR Control (IVVC). In addition to the traditional benefits achieved through CVR, VVO technologies can improve distribution system reliability and mitigate the impacts of distributed energy resources (e.g., photovoltaics (PV), etc.).
When applied to an electric distribution system, CVR can achieve peak demand reduction and energy savings of up to 5 percent. When treated as an energy efficiency measure, the business case of CVR is significantly affected by the amount of voltage reduction that any particular technology can achieve through its control algorithms.
Traditional methods of CVR, although capable of achieving nominal voltage reduction, often have done so at the expense of increased voltage regulator (i.e., on-load tap changing transformer or auto-regulating voltage transformer) tap change operations. Moreover, many traditional methods do not provide reliability benefits and cannot deal with the real-time, intermittent and complex nature of the modern grid.
Traditional Power Flow-based Approaches to CVR
Several traditional methods exist for implementing CVR and more recently VVO, and most are based on power flow modeling of electric distribution circuits.
Simple voltage reduction. In the most basic approach, a simple power flow model is run to determine voltage delivery requirements at peak load (i.e., under worst-case conditions). An automatic voltage regulator (AVR) control then is programmed with the lowest possible voltage set point necessary to accommodate the peak-loading scenario and will maintain that voltage at the substation bus 24/7.
Line drop compensation. Adding one level of complexity, line drop compensation (LDC) uses power flow modeling to calculate the voltage drop along the length of an electric distribution feeder by using line resistance (R) and line reactance (X) factors, combined with measured current. The R and X values are input to the AVR control, which then adjusts the voltage to the minimum required based on the measured current at the substation bus.
Distribution management systems. Distribution management systems (DMS) provide utilities with a method for fully automating power flow model-based CVR and VVO. Using switching information that is updated in real time, DMS network models allow power flows to be run on the current state (or topology) of the distribution grid, providing more accurate results.
Challenges Presented by the Modern Grid
Historically, traditional power flow modeling and voltage control techniques have been sufficient for distribution system control: delivery of a service voltage within a defined range, one-way power flow and an unengaged energy consumer. The recent modernization of the electric grid and its goals require more advanced management and control of the electric grid than what has been available to utilities.
One of the primary focuses of grid modernization is to enable the integration of customer-owned distribution generation resources such as PV and wind power. Many issues created by these new generation sources can affect reliable grid operations: reverse power flow, voltage spikes and sags, extended periods of high voltage, increased tap change operations and increased capacitor switching. To complicate matters further, these resources are intermittent and often exhibit random behavior. Although utilities must accommodate any injection of power back into their distribution grids, they are unable to take control of and dispatch these generation sources.
Other challenges the modern grid presents lie within business and societal impacts. Many grid modernization goals are designed to provide social and business benefits. Transactive pricing, for example, will allow consumers to engage in energy markets. Social networking technologies allow consumers to become engaged immediately in decisions that affect their energy costs.
“Current power system controls do not address the grid requirements to achieve existing policy mandates for renewable and distributed resources and responsive customer demand,” said Jeffrey Taft, chief architect for electric grid transformation at Pacific Northwest National Laboratory.
Advanced VVO technology, which is based on signal processing and adaptive control techniques, has been deployed on more than 200 North American electric distribution circuits. In all of those applications, the technology demonstrated an ability to maximize voltage reduction and reduce voltage regulator operations. In addition, more recent deployments have demonstrated the ability to mitigate the negative impacts of intermittent PV energy sources on distribution system performance.
Jeremy Wilson is co-founder and director of technical sales at Utilidata Inc., where he develops partner relationships and alliance agreements with large utilities and smart grid vendors and works with regional energy authorities to advance regulatory framework for volt/VAR optimization. He has a bachelor’s degree from Washington State University.